I'm currently trying to sort out my dual booting for Windows and Ubuntu (and I don't do much at all with Linux). This used to work like a charm, then Ubuntu updated, and it just goes to a grub prompt now. I tried reinstalling it and it did the same, so I wiped both my SSD's so it was completely fresh and started totally from scratch, stuck Ubuntu on using the "Install alongside Windows" option, and I'm back to grub so I'm guessing it's more BIOS related but it's weird that this happened after I went into Ubuntu fine and did an update.
When I try to list drives, it's only seeing the main one, not the second bay so I assume that's part of the issue as it looks like ubuntu very cleverly used the spare partition that I created on that drive as I can see the various Ubuntu folders there when I boot into a Live USB session.
BIOS does know that that drive is there as far as I can tell. When I was playing with various install options before, it came up as a bootable device with ubuntu on, but went to Grub.
I've tried disabling secure boot, enabling legacy boot, and disabling fast boot in Windows. I've seen some stuff about pointing grub to the boot folder, but this is on the second drive which it can't see. Also tried the Ubuntu Boot-Repair but had no luck on that front.
When it boots up into the Grub (as should be Ubuntu) it is currently pointing to the boot manager on the main drive.
I didn't know what information would be useful, so apologies if this is a bit sparse! Let me know what you need and I can see if I can get it.